Since the lithium-ion secondary battery has been commercialized, due to advantages, such as a high energy density, a high operating voltage, none memory effect and the like, the lithium-ion secondary battery is widely used as a power supply for various mobile devices. With large scale applications of the lithium-ion secondary battery, the cycle life and the safety problem of the lithium-ion secondary battery are increasing significantly.
The lithium-ion secondary battery mainly comprises a positive electrode plate, a negative electrode plate, a separator and an electrolyte. The separator is provided between the positive electrode plate and the negative electrode plate, and mainly functions to: (1) physically isolate the positive electrode plate and the negative electrode plate of the lithium-ion secondary battery so as to prevent an interior short circuit between the positive electrode plate and the negative electrode plate; (2) ensure the lithium ions to pass the electrolyte uniformly and move back and forth freely between the positive electrode plate and the negative electrode plate; (3) absorb the electrolyte and keep the electrolyte to make the lithium-ion secondary battery have a longer cycle life.
At present, most of the separators used in the lithium-ion secondary battery are polyolefin membranes, such as polyethylene (PE) membrane, polypropylene (PP) membrane or polypropylene/polyethylene/polypropylene (PP/PE/PP) composite membrane, when the lithium-ion secondary battery is abused (such as overcharge, thermal shock or puncture and the like), the temperature of the lithium-ion secondary battery generally will rise to be equal to or more than 90° C., once the interior temperature of the lithium-ion secondary battery is more than 90° C., the conventional polyethylene (PE) membrane or polypropylene (PP) membrane will have a more serious thermal shrinkage, a short circuit would be established between the positive electrode plate and the negative electrode plate and more heat would be generated, the lithium-ion secondary battery would be easily fired or even exploded. Furthermore, a surface tension of the polyolefin membrane is too low, the polyolefin membrane has too poor infiltration capability and absorption capability on the carbonate electrolyte used in the lithium-ion secondary battery, and can not meet the requirement of a longer cycle life of the lithium-ion secondary battery.
Regarding this situation, a known manner is performed so that a ceramic layer is coated onto the separator so as to reduce the thermal shrinkage and prevent the short circuit between the positive electrode plate and the negative electrode plate and improve the infiltration capability of the separator on the electrolyte. However, the main material of the ceramic layer generally comprises ceramic particles with a very high hardness such as aluminum oxide and the like, which will increase the wear of the coating machine and the cutting machine, and increase the production cost, and has a limited ability to increase the retention performance on the electrolyte, and cannot meet the requirement of a longer cycle life of the lithium-ion secondary battery, and also can not achieve a better inhibitory effect on the abused situations such as overcharge and the like. The reason is that when the lithium-ion secondary battery is abused, although the ceramic layer may reduce the heat shrinkage of the separator, the ceramic layer can not prevent the temperature of the lithium-ion secondary battery from increasing until the separator is melt, and the integrity of the ceramic layer will also be damaged, the short circuit between the positive electrode plate and the negative electrode plate occurs, finally the lithium-ion secondary battery will be fired or even exploded. Moreover, since the ceramic particle has a solid structure, the retention performance of the ceramic layer on the electrolyte is limited.